Hybrid optical antenna with high directivity gain

摘要

Coupling between electronic state and far field light, including absorption and spontaneous emission, is a central issue for applications such as quantum metrology, optical quantum information, single molecule fluorescence spectroscopy, and ultra sensitive detection which demand on high quantum efficiency. In such applications, propagating far field light with diffraction limited spatial distribution has to be coupled to the electronic state of a quantum absorber/emitter with a size far below the diffraction limit. Such a significant contrast between the wavelengths of photon and electron sets limitations on the light-matter interaction strength. The most straight forward solution is to convert far-field modes to near-field modes with dimensional scale closer to the electronic state. The process of converting far field to near field and vice versa can be conducted by an antenna as an intermediate element between far field mode and electronic state in a quantum element (absorber/emitter). Here, we classify optical antenna based on their performance into three categories. Considering each category advantage, we propose a hybrid antenna with superior performance. A quantum efficiency of about 50% is predicted for a semiconductor with volume of ～λ~3/170. Despite the weak optical absorption coefficient of 2000 cm~(-1) in the long infrared wavelength of ～8 μm, very strong far-filed coupling has been achieved, as evidenced by an axial directivity gain of 16 dB, which is only 3 dB bellow of theoretical limit.